Oscillator proximity detector with removable interchangeable sensing heads

ABSTRACT

An electric proximity detector or switch for detecting the presence or absence of electrically conductive objects is provided with interchangeable sensing heads arranged to be removably mounted on a basic switch unit or to be positioned at a location remote from the basic switch unit as desired.

llite States ntnt Clarke 1 1 arch 6 1973 15 1 OSCILLATOR PROXIMITTY DETECTOR 3,521,184 7 1970 Bowker ..33I/65 WITH REMOVABLE 3,504,236 3 1970 Miyagawa et a1. ..340/258 c x INTE CHA GE L SE S NG H DS 3,013,256 12/1961 Damast ..331/65 X 2,379,664 7/1945 Stanko ..336/90 [75] Inventor: Geoffrey Clarke, Blunsdon, near Swmdon England Primary Examiner-Roy Lake [7 3] Assignee: Square B Company, Park Ridge, 11]. Assistant ExaminerSiegfried H. Grimm Filed: J 1971 i/:1t;0rneyHaroId J. Rathbun and W1II1am H. Schmel- [21] Appl. No.: 108,915

[57] ABSTRACT [30] Foreign Application Priority Data An electric proximity detector or switch for detecting March 5 1970 Great Britain ..10 567/70 the Presence or absence of electrically conductive I jects is provided with interchangeable sensing heads 52 us. Cl. ..3311/65, 324/40, 331/66, arranged be removabIy mounted on a basic Switch 33 33 3 5 C unit or to be positioned at a location remote from the 51 Int. ci. ..G01v 3/10, H036 5/08 basic Switch unit as desired [58] Field of Search .331/65, 66; 324/40, 41; 336/90, 212; 340/258 C 4 Claims, 16 Drawing Figures [56] References Cited UNITED STATES PATENTS 3,601,691 8/1971 Gardiner ..324/41 X r -r T 3| 1'2 I 25 I H0 1? I i 1 1 1 L 1 I ,1 T i OSCILLATOR OUTPUT UNIT l I l\ I (/I -I I. I I 26 .1 '1 I g J. 14 30 I I 15 DETECTOR CONVERTER T I I I I I 2I\1 I I I T 29 28 24 22 20 IO PATENTEUHAR 61975 3 719, 9

SHEET 20F 3 FIG. FIG. 7

1 3+ m '1 t "IIH I 22 FIG. 6

INVENTOR. GEOFFREY CLARKE QTQWY'H 4 PATENTEUHAR 6 I975 SHEET 3 OF 3 I sa INVENTOR. GEOFFREY CLARKE ()SQILLATOR PROXUWITY DETECTOR WITH REMOVABLE INTERCIIANGEABLE SENSING HEADS This invention relates to electric proximity detectors or switches for detecting the presence or absence of electrically conductive objects, and more particularly to a proximity switch having interchangeable sensing heads arranged to be removably mounted on a basic switch unit or to be positioned at a location remote from the basic switch unit as desired.

Proximity detectors or switches are devices having an output state determined by the presence or absence of electrically conductive material proximate to a sensing coil of the device. A known form of proximity switch comprises a sensing coil forming part of an oscillator, a detector which responds to changes in amplitude or phase of the current in the oscillator resulting from a change in the electrical condition of the sensing coil, an output unit which translates signals from the detector into information recognizable by equipment controlled by the proximity switch, and a power supply to feed the foregoing switch components. Such a proximity switch is disclosed, for example, in U.S. Pat. No. 3,521,184, issued to Anthony J. Bowker on July 21, 1970. The switch of the prior patent, however, has only one size of sensing coil and it is in fixed position within the basic switch unit. It is desirable to have several different interchangeable sensing heads each containing a sensing coil of selected size thereby to provide a wide variation in sensitivity, which increases with increasing coil size, and to be able to position the sensing heads either locally in one or more positions on the basic switch unit or remotely at locations remote from the basic switch unit. It is also desirable to have sensing heads of different shapes to facilitate the positioning thereof at the region to be sensed.

In accordance with the present invention, there is provided a proximity switch using transformer action to energize either local or remote sensing heads of different shapes and which may include sensing coils of different sizes. Because of the transformer coupling, there can be complete physical isolation between the sensing coil and the associated switch circuitry. Such complete physical isolation simplifies the protective enclosure for the basic switch unit by eliminating the need for a cable entry from a remote sensing head. There is also electrical isolation between the basic switch unit and the sensing head. This eliminates the need for an isolation transformer in the power supply for the switch.

The transformer coupling of the present switch is such that there is an inherent limitation in the amount of energy which can be transformed from the basic switch unit to a coupling coil of a coupling unit and, hence, to the sensing coil of-a sensing head. This is of advantage when the switch is used in explosive atmospheres.

Further, the body of the basic switch unit is so designed that different sensing heads, each including a transducer sensitive to an external stimulus, may be readily interchanged and either mounted on the coupling'unit locally in different relative positions with respect to the basic switch unit or positioned remotely, thus allowing a standardized switch to fulfill a wide range of applications merely by the substitution of different sensing heads to respond to different external stimuli, such as changes in temperature, light intensity, capacitance or inductance. The basic switch unit may also be used as a proximity detector without a separate sensing head.

Other objects and advantages of this invention will become apparent from the following specification wherein reference is made to the drawings, in which:

FIG. 1 is a schematic view partly in block form showing a proximity switch in accordance with this invention including a local sensing head;

FIG. 2 is a fragmentary schematic view of the proximity switch of FIG. 1 including a remote sensing head;

FIG. 3 is a rear end view, before encapsulation, of a coupling member forming part of a proximity switch in accordance with this invention and showing a portion of a relatively large sensing head;

FIG. 4 is a sectional view taken generally along the line 4-4 of FIG. 3, with the coupling member attached to a switch unit;

FIG. 5 is a top view of a proximity switch in accordance with this invention showing the relatively large sensing head mounted at the top thereof;

FIG. 6 is a side view of the switch of FIG. 5;

FIG. 7 is an end view of the switch of FIG. 5;

FIG. 8 is a view similar to FIG. 6 showing the relatively large sensing head mounted at an end face of the switch instead of at the top;

FIG. 9 is an end view of the relatively large sensing head of FIGS. 3 to 8 with part of a cover broken away;

FIG. 10 is a sectional view taken generally along the line 10-10 of FIG. 9;

FIG. 11 is a perspective view of the limit switch of FIGS. 5 to 8 including a connecting plug for a coaxial cable leading to a relatively large remote sensing head;

FIG. 12 is a sectional view of a detail of the relatively large remote sensing head of FIG. 1 1;

FIG. 13 is a perspective view of the connecting plug of FIG. 11 and a relatively small remote sensing head;

FIG. 14 is a sectional view of the relatively small remote sensing head taken generally along the line 14- 14 of FIG. 13;

FIG. 15 is a sectional view of the connecting plug taken generally along the line 15-15 of FIG. 13', and

FIG. 16 is a schematic view similar to FIG. 1 and 2 showing a pair of remote sensing heads so connected that the proximity switch performs a logic function.

Referring to FIG. 1, a basic proximity switch unit 10 in accordance with this invention comprises an oscillator 11 supplied from a supply source indicated as a supply cable 14 and including a sensing coil 11a sensitive to electrically conductive objects proximate thereto. The oscillator 11 feeds a detector 15, and signals from the detector 15 control an output unit 16 which is supplied from the cable 14 through a dc-dc converter 18. The sensing coil 11a is wound on a magnetizable core 1%. The foregoing components are enclosed within an enclosure 20 having an opening for an output cable 21 leading from the output unit 16. The basic switch unit such as the unit 10 shown diagrammatically in FIG. 1 is fully described in U.S. Pat. No. 3,521,184, supra. As explained in the patent, a change in the electrical condition of the coil 11a causes a change in an output signal in the output cable 21.

The switch unit is arranged to removably mount a coupling member 22 comprising an enclosure 24, a magnetizable core 19b, a transformer or coupling coil 25 wound on the core 19b, and a capacitor 26 connected in parallel with the coil 25. The cores 19a and 19b are so arranged that when the coupling member 22 is mounted on the switch unit 10 their pole faces are in juxtaposed relationship to form a transformer 19 having a magnetic path of relatively low reluctance.

The coupling member 22 is arranged to removably mount a sensing head 28 which, in the embodiment illustrated, comprises and enclosure 29, a magnetizable core 30, and a sensing coil 31 wound on the core 30. As shown, the coils 25 and 31 are connected in a loop circuit with each other.

Referring now to FIG. 2, a connecting plug 32 including an enclosure 34 is shown as mounted on the coupling member 22 in place of the sensing head 28 of FIG. 1. The connecting plug 32 serves to connect the terminals of the coil 25 respectively to an inner conductor 35a and an outer conductor 35b of a coaxial cable 35 extending through an opening in the enclosure 34. The other end of the coaxial cable 35 enters an enclosure 36 of a remote sensing head 38 wherein the inner and outer conductors 35a and 35b of the cable 35 are connected respectively to the terminals of a sensing coil 40 wound on a magnetizable core 41.

It will be apparent from FIGS. 1 and 2 that any electrically conductive object brought near the core 30 or the core 41 will change the electrical condition of the coil 11a thereby to cause an increase in the losses in the tank circuit Ila-11 causing the control components of the basic switch unit 10 to alter a signal in the output cable 21 as explained more fully in U.S. Pat. No. 3,521,184, supra.

The coil 25 and core 19b together with coil 31 and core 30 (or coil 40 and core 41) constitute a load on the tank circuit lla-ll and the capacitor 26 serves to reduce this load by tuning the coils 25 and 31 (or 40) and thereby improve the response of the detector.

In the remaining figures of the drawings wherein physical embodiments of the invention are shown, parts corresponding to the parts shown schematically in FIGS. 1 and 2 are referred to by the same reference characters.

Referring now to FIGS. 3 and 4, the coupling member 22 comprises a molded insulating block 42 positioned within the housing 24 and provided, in a thickened upper portion 45, with a pair of laterally spaced, rearwardly opening recesses 46 which receive a pair of L-shaped terminals 48. The housing 24 is preferably an open-ended rectangular tube made of non-magnetizable metal. Each of the terminals 48 has an upwardly directed threaded socket 49 accessible through a respective one of a pair of aligned openings 50in the upper portion 45 of the block 42 and a respective one of a pair of aligned openings 51 in a top wall 52 of the housing 24, and a forwardly directed threaded socket 53 accessible through respective one of a pair of aligned openings 54 in the block portion 45.

In FIGS. 3 and 4, the sensing head 28 is shown mounted on the top of the coupling member 22 as shown also in FIGS. 5, 6, and 7, and is hereinafter considered to be a relatively large sensing head. Two prong terminals 56 (see also FIGS. 9 and 10) of the sensing head 28 are received respectively in the sockets 49 0f the terminals 48 and are secured by set screws 58 threaded into the respective sockets 53. Outer end faces of the set screws 58 are covered by respective non-metallic sealing screws 59 having large head portions disposed respectively within the openings 54. The sensing head 28 is further secured in position by a screw 60 passing through a central opening 61 therein (see FIGS. 9 and 10) and received in a threaded opening in an upper insert 62 exposed through an opening in the wall 52 and retained in the block 42.

It will be apparent that the sensing head 28 can alternatively be mounted on the front face of the coupling member 22, as indicated schematically in FIG. 1 and shown in FIG. 8, with the prong terminals 56 received respectively in the sockets 53 and held by the set screws 58 threaded into the respective sockets 49, the screws 58 being covered by the sealing screws 59, and with the screw 60 received in a threaded opening in a front insert 63 retained in the block 42.

The core 19b, which is mounted on the rear of the block 42, is generally cylindrical with four peripherally spaced slots and defines an annular coil space which receives the coil 25. The opposite ends of the coil 25 are connected respectively to the L-shaped terminals 48 which may have respective depending prong connectors 48a for this purpose. The capacitor 26 is also connected across the prong connectors 48a as indicated.

After the parts within the housing 24 are assembled as shown in FIGS. 3 and 4, the rear-end portion of the housing 24 is filled with a suitable insulating material such as an epoxy resin which covers the pole faces of the core 19b, the coil 25, the rear faces of the terminals 48 and the capacitor 26, and which retains the core 19b, the coil 25, and the capacitor 26 in position.

A pair of mounting holes 65 extending through diagonally opposite corners of the coupling member 22 receive screws 66 (FIGS. 7 and 11) which thread into inserts, not shown, positioned behind a plastic cover portion 20a of the enclosure 20 in the basic switch unit 10 to removably secure the member 22 to the switch unit 10. As shown most clearly in FIG. 4, the annular core 19b of the coupling member 22 is aligned with the annular core 19a of the switch unit 10 when the unit 10 and the member 22 are secured together, it being understood that the core 19a is slotted as the core 19b and that the slots of one are in alignment respectively with the slots of the other.

Referring now to FIGS. 9 and 10, the housing 29 of the relatively large sensing head 28 comprises a cylindrical tubular portion 290 and a cover 29b, both preferably being of non-magnetizable metal. The core 30 defines an annular coil space which receives the coil 31 and fits snugly within the housing portion 29a with the outer end portions of its inner and outer poles 30a and 30b extending forwardly from the housing portion 29a. The core 30 has an axial opening 30c for receiving the mounting screw 60 and four peripherally spaced slots 30d similar to the slots in the cores 19a and 19b.

Received respectively in the upper two of the slots 30d as viewed in FIG. 9 are two coil terminals 67 each having an axial portion 67a to which a respective one of the two ends of the coil 31 is electrically secured and a radial portion 67b having a widened portion 670 to which a widened inner end portion 56a of one of the prong terminals 56 is secured as by a screw 68. I

A knockout indicated by broken lines at 69 in FIG. 9 and containing the opening 61 has been removed from the central portion of the cover 29b in FIG. 10 to provide an enlarged opening 70 for passage of the terminals 56 and the screw 60. A smaller circular knockout 71' for a purpose to be described is formed in the housing portion 29a near a locating nib 72 on the cover 29b. A pair of locating projections 74 on the cover 29b engage the sides of the coupling unit 22 when the sensing head 28 is mounted thereon, or may be received in complementary recesses in a mounting surface (not shown) when the sensing head 28 is used as a remote sensing head.

After the parts of the sensing head 28 are assembled within the housing 29, the housing is filled with epoxy and the epoxy is molded to form a cover 75 over the protruding portions of the core 30 and the coil 31 or a separate molded cover may be used.

When a relatively large sensing head is to be used remotely as shown in FIG. 11, the sensing head 28 may be modified to form the head 38. The knockout 71 instead of the knockout 69 isremoved to permit entry of the coaxial cable 35. For remote use, the terminals 56 shown in FIG. 10 are omitted as indicated in FIG. 12 and connection is made from the inner and outer conductors 35a and 35b of the cable 35 directly to the coil terminals 67 by means of the screws 68. The other end of the cable 35 in FIG. 11 is connected to the coil 25 of the coupling member 22 by the connecting plug 32.

The connecting plug 32, shown best in FIG. comprises a block 32a molded of insulating material having a pair of prong terminals 76 extending from one end and connected respectively internally of the block 32a to the inner and outer conductors 35a and 35b of the cable 35 which enters the block at the opposite end. The prong terminals 76 are electrically connected to the terminals of the coil 25 of the coupling member 22 when they are respectively received in the sockets 49 or 53 and secured by the set screws 58 as in the case of the sensing head 28. An opening 78 through the block 32a is provided for a mounting screw which may be threaded into either of the inserts 62 or 63. The block 32a corresponds to the enclosure 34 of FIG. 2.

Although each of the sensing heads 28 and 38 may be made in various sizes, they may be considered to be relatively large as hereinbefore explained. Referring now to FIG. 13, a relatively small remote sensing head 80 is shown connected to the connecting plug 32 through the coaxial cable 35. The relatively small remote sensing head 80 comprises a non-magnetizable tubular metal enclosure 83 (FIG, 14) having a magnetizable core 84 secured atone end portion and enclosing a coil 85 connected to inner and outer conductors 35a and 35b of the cable 35. The cable enters the enclosure 83 at the opposite end from the core 84 and is secured against retraction by a wire retainer. The wire retainer comprises an inwardly protruding portion 88a of a non-metallic closure plug 88 which fits snugly into the enclosure 83 and covers the pole faces of core 84. As shown in the drawing, the inner wire 35a of the cable 35 is received through an opening in the protruding portion 88a. The other end of the housing 83 is closed by a bushing 89.

Although the cores 19a, 19b, 30, 41, and 84 may be made from any suitable magnetizable material, they are preferably of ceramic material.

Although the L-shaped terminals 48 are shown with depending prong connectors 48a these may be omitted, the coil and the capacitor 26 being connected directly to the terminals 48.

It is to be understood that sealing gaskets may be used where necessary, for example, between the coupling member 22 and the sensing head 28.

When it is desired to have the proximity switch provide a logic function, such as an OR or AND function, two or more of the remote sensing heads such as the heads 38 may be connected in series or parallel with each other by means of a four-way terminal block 90 as indicated in FIG. 16 which shows the connection for an OR function. The coaxial cable 35 extends from the connecting plug 32 to the terminal block 90 and coaxial cables 91 and 92 extend from the terminal block 90 to the remote sensing heads 38, respectively.

When it is desired to have the proximity limit switch perform an AND function, the connections inside of the terminal block 90 may be changed.

The switch 10 with its coupling unit 22 can be used for purposes other than detecting the proximity of conductive material, by using them in conjunction with sensing heads containing other forms of transducer instead of the sensing coil 40 or 31.

It is merely necessary to select component values so that the oscillations in the tuned tank circuit Ila-ill are damped as a result of a change in the electrical state of the transducer. Thus, for example, the sensing head could comprise a thermistor to detect a temperature change, or a photoconductive cell to detect a light source. Similarly changes in capacitance or inductance could be detected.

I claim:

1. An electrical proximity switch comprising an enclosed switch unit including a first sensing coil sensitive to electrically conductive objects proximate thereto and means responsive to changes in the electrical condition of the first sensing coil to provide an output signal, the first sensing coil being wound on a magnetizable core, a coupling member including an enclosure having disposed therein a coupling coil wound on a magnetizable core, means for removably mounting the coupling member on the switch unit with the coupling coil in inductive relationship with the first sensing coil, a sensing head including an enclosure having disposed therein a second sensing coil sensitive to electrically conductive objects proximate thereto and wound on a magnetizable core, and means for removably mounting the sensing head on the enclosure of the coupling member selectively in more than one position with respect thereto with the second sensing coil connected in a loop circuit with the coupling coil, whereby a change in the electrical condition of the second sensing coil causes a change in the electrical condition of the first sensing coil.

2. A proximity switch in accordance with claim 1 wherein said means for removably mounting the sensing head on the enclosure of the coupling member selectively in more than one position with respect thereto comprises a pair of intersecting threaded openings in said enclosure of the coupling member,

prong means on said sensing head for insertion selectively into said openings, and fastening means threadably insertable selectively into said openings, the fastening means being threadably inserted into one of said openings to engage said prong means when the prong means is inserted into the other of said openings.

3. A proximity switch in accordance with claim 1 including a relatively large sensing head, a relatively small sensing head, and means for selectively and interchangeably mounting said sensing heads on said enclosure of the coupling member.

4. An electrical proximity switch comprising an enclosed switch unit includinga first sensing coil sensitive to electrically conductive objects proximate thereto and means responsive to changes in the electrical condition of the first sensing coil to provide an output signal, the first sensing coil being wound on a magnetizable core, a coupling member including and enclosure having disposed therein a coupling coil wound on a magnetizable core, means for removably mounting the coupling member on the switch unit with the coupling coil in inductive relationship with the first sensing coil, a relatively large sensing head and a relatively small sensing head each including an enclosure having disposed therein a sensing coil sensitive to electrically conductive objects proximate thereto and wound on a magnetizable core, and means for selectively and interchangeably mounting said sensing heads on the enclosure of the coupling member with the sensing coil of the mounted sensing head connected in a loop circuit with the coupling coil, whereby a change in the electrical condition of the sensing coil of the mounted sensing head causes a change in the electrical condition of the first sensing coil. 

1. An electrical proximity switch comprising an enclosed switch Unit including a first sensing coil sensitive to electrically conductive objects proximate thereto and means responsive to changes in the electrical condition of the first sensing coil to provide an output signal, the first sensing coil being wound on a magnetizable core, a coupling member including an enclosure having disposed therein a coupling coil wound on a magnetizable core, means for removably mounting the coupling member on the switch unit with the coupling coil in inductive relationship with the first sensing coil, a sensing head including an enclosure having disposed therein a second sensing coil sensitive to electrically conductive objects proximate thereto and wound on a magnetizable core, and means for removably mounting the sensing head on the enclosure of the coupling member selectively in more than one position with respect thereto with the second sensing coil connected in a loop circuit with the coupling coil, whereby a change in the electrical condition of the second sensing coil causes a change in the electrical condition of the first sensing coil.
 1. An electrical proximity switch comprising an enclosed switch Unit including a first sensing coil sensitive to electrically conductive objects proximate thereto and means responsive to changes in the electrical condition of the first sensing coil to provide an output signal, the first sensing coil being wound on a magnetizable core, a coupling member including an enclosure having disposed therein a coupling coil wound on a magnetizable core, means for removably mounting the coupling member on the switch unit with the coupling coil in inductive relationship with the first sensing coil, a sensing head including an enclosure having disposed therein a second sensing coil sensitive to electrically conductive objects proximate thereto and wound on a magnetizable core, and means for removably mounting the sensing head on the enclosure of the coupling member selectively in more than one position with respect thereto with the second sensing coil connected in a loop circuit with the coupling coil, whereby a change in the electrical condition of the second sensing coil causes a change in the electrical condition of the first sensing coil.
 2. A proximity switch in accordance with claim 1 wherein said means for removably mounting the sensing head on the enclosure of the coupling member selectively in more than one position with respect thereto comprises a pair of intersecting threaded openings in said enclosure of the coupling member, prong means on said sensing head for insertion selectively into said openings, and fastening means threadably insertable selectively into said openings, the fastening means being threadably inserted into one of said openings to engage said prong means when the prong means is inserted into the other of said openings.
 3. A proximity switch in accordance with claim 1 including a relatively large sensing head, a relatively small sensing head, and means for selectively and interchangeably mounting said sensing heads on said enclosure of the coupling member. 